Fix infloop in redisplay due to truncated lines and invisible text

Fix infloop in redisplay due to truncated lines and invisible text

* src/xdisp.c (forward_to_next_line_start): Don't call
'get_next_display_element' after finding the end of line.  This
avoids setting the row's end position to the wrong value when the
next screen line begins with invisible text; that wrong value
caused set_cursor_from_row position the cursor in the wrong screen
line, and eventually triggered bug#24109.